* java.util.concurrent.CompletableFuture#thenAcceptAsync}.
   *
   * @param callback The callback to invoke when this {@code Future} is completed.
   * @param executor The executor to run {@code callback} when the future completes.
   */
  public final void addCallback(FutureCallback<? super V> callback, Executor executor) {
    Futures.addCallback(this, callback, executor);
  }

  public void testOr_supplier_present() {
    assertEquals("a", Optional.of("a").or(Suppliers.ofInstance("fallback")));
  }

  public void testOr_supplier_absent() {
    assertEquals("fallback", Optional.absent().or(Suppliers.ofInstance("fallback")));
  }

  public void testOr_nullSupplier_absent() {

  public void testOr_supplier_present() {
    assertEquals("a", Optional.of("a").or(Suppliers.ofInstance("fallback")));
  }

  public void testOr_supplier_absent() {
    assertEquals("fallback", Optional.absent().or(Suppliers.ofInstance("fallback")));
  }

  public void testOr_nullSupplier_absent() {

    // cipher is added to signal that a protocol fallback has taken place.
    val supportedCipherSuites = sslSocket.supportedCipherSuites
    val indexOfFallbackScsv =
      supportedCipherSuites.indexOf(
        "TLS_FALLBACK_SCSV",
        CipherSuite.ORDER_BY_NAME,
      )
    if (isFallback && indexOfFallbackScsv != -1) {
      cipherSuitesIntersection =

    expectedCipherSuites.add(CipherSuite.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA.javaName)
    if (listOf<String>(*socket.supportedCipherSuites).contains("TLS_FALLBACK_SCSV")) {
      expectedCipherSuites.add("TLS_FALLBACK_SCSV")
    }
    assertThat(socket.enabledCipherSuites)
      .containsExactly(*expectedCipherSuites.toTypedArray())
  }

  @Test
  fun tls_explicitCiphers() {

## Version 5.0.0-alpha.4

_2022-02-01_

**This release introduces fast fallback to better support mixed IPv4+IPv6 networks.** Fast fallback
is what we're calling our implementation of Happy Eyeballs, [RFC 8305][rfc_8305]. With this
feature OkHttp will attempt both IPv6 and IPv4 connections concurrently, keeping whichever connects
first. Fast fallback gives IPv6 connections a 250 ms head start so IPv6 is preferred on networks

     * potential NTLM fallback (if the server does not support kerberos).
     * 
     * @param subject
     *            represents the user who perform Kerberos authentication. Should at least contain a TGT for the user.
     * @param domain
     *            domain for NTLM fallback
     * @param username
     *            user for NTLM fallback
     * @param password

        private final ArtifactRepositoryLayout fallback;

        UnknownRepositoryLayout(String id, ArtifactRepositoryLayout fallback) {
            this.id = id;
            this.fallback = fallback;
        }

        public String getId() {
            return id;
        }

        public String pathOf(Artifact artifact) {
            return fallback.pathOf(artifact);
        }

	defer cancel()

	// Keep track of fallback disks
	var fdMu sync.Mutex
	fds := opts.fallbackDisks
	fallback := func(err error) StorageAPI {
		if _, ok := err.(StorageErr); ok {
			// Attempt to grab a fallback disk
			fdMu.Lock()
			defer fdMu.Unlock()
			if len(fds) == 0 {
				return nil
			}
			fdsCopy := fds
			for _, fd := range fdsCopy {
				// Grab a fallback disk
				fds = fds[1:]

      "kubeconfig": "__KUBECONFIG_FILEPATH__",
      "cni_bin_dir": "/opt/cni/bin",
      "exclude_namespaces": [ "istio-system" ]
  }
}
`
)

func getEnv(key, fallback string) string {
	if value, ok := os.LookupEnv(key); ok {
		return value
	}
	return fallback
}

func setEnv(key, value string, t *testing.T) {
	t.Helper()
	err := os.Setenv(key, value)
	if err != nil {